1. Field of the Invention
Aspects of the present invention relate to a method of fabricating a multi-freestanding GaN wafer, and more particularly, to a method of producing a freestanding GaN wafer on a large scale.
2. Description of the Related Art
A variety of methods of fabricating GaN for use in a substrate for a blue and UV-based light emitting device have been proposed. In most conventional methods of fabricating GaN, porous GaN is formed on a substrate, such as an SiC substrate or a sapphire substrate, thick GaN is grown on the porous GaN and is lifted off using a UV laser etc., thereby obtaining freestanding GaN.
Mynbaeva et al. suggest a method of growing GaN on an SiC substrate. In this method, an HF solution is used in a UV excitation atmosphere so that porous GaN is used. Thus, the method requires an additional wet etching process except for a process of forming a layer. As a result, additional processes including a cleaning process are complicated (Strain Relaxation in GaN Layers Grown on Porous GaN Sublayers, MRS Internet J. Nitride Semicond. Res. 4, 14, 1999).
Xiuling Li et al. suggest a method of forming porous GaN using metal-assisted electroless wet etching using metal such as Pt, etc. This method also requires additional processes of forming a metallic layer and etching. Thus, processes are complicated (In-plane Bandgap Control in Porous GaN through Electroless Wet Chemical Etching, Volume 80, Number 6, 11 Feb. 2002, Applied Physics Letters).
As described above, a variety of methods of separating thick GaN grown on another substrate have been proposed. As an example thereof, a UV laser is heated in a state where the entire substrate is heated to about 1000° C. so that GaN is separated from a sapphire substrate, etc. It takes several repetitions to be able to perform the lift-off operation using UV rays and heat. Furthermore, in the conventional lift-off method, for reasons including thermal imbalance, etc., the probability that a GaN layer may be broken during the lift-off operation is high.
Yuichi Oshima et al. suggest a method of void assisted separation (VAS) (Preparation of Freestanding GaN Wafers by Hydride Vapor Phase Epitaxy with Void-Assisted Separation, Jpn. J. Appl. Phys. Vol. 42, 2003, pp. L1-L3, Part 2, No. 1A/B, 15 Jan. 2003). In this method, an ex-situ TiN nanonet is formed on a GaN template substrate so that porous GaN can be easily separated from the GaN template substrate, and then, thick GaN is separately formed. In the method, comparatively good freestanding GaN can be obtained. However, the process is complicated, metallic contamination may occur, and the cost is high.